The Oxidative Stress of Hyperhomocysteinemia Results from Reduced Bioavailability of Sulfur-Containing Reductants

ABSTRACT

Vegetarian subjects consuming subnormal amounts of methionine (Met) are characterized by subclinical protein malnutrition causing reduction in size of their lean body mass (LBM) best identified by the serial measurement of plasma transthyretin (TTR). As a result, the transsulfuration pathway is depressed at cystathionine-β-synthase (CβS) level triggering the upstream sequestration of homocysteine (Hcy) in biological fluids and promoting its conversion to Met. Maintenance of beneficial Met homeostasis is counterpoised by the drop of cysteine (Cys) and glutathione (GSH) values downstream to CβS causing in turn declining generation of hydrogen sulfide (H2S) from enzymatic sources. The biogenesis of H2S via non-enzymatic reduction is further inhibited in areas where earth’s crust is depleted in elemental sulfur (S8) and sulfate oxyanions. Combination of subclinical malnutrition and S8-deficiency thus maximizes the defective production of Cys, GSH and H2S reductants, explaining persistence of unabated oxidative burden. The clinical entity increases the risk of developing cardiovascular diseases (CVD) and stroke in underprivileged plant-eating populations regardless of Framingham criteria and vitamin-B status. Although unrecognized up to now, the nutritional disorder is one of the commonest worldwide, reaching top prevalence in populated regions of Southeastern Asia. Increased risk of hyperhomocysteinemia and oxidative stress may also affect individuals suffering from intestinal malabsorption or westernized communities having adopted vegan dietary lifestyles.